1. Field of the Invention
The present invention relates to a reader for reading an indicia, for example a reader for reading bar code symbols on products at a point of sale transaction terminal.
2. Discussion of the Prior Art
In prior art readers comprising a scanner and a decoder, the scanner generates a scanning spot which traverses the target indicia such as a bar code symbol and light reflected from the bar code symbol is received by the decoder wherein a digital electrical signal is generated and analyzed to decode the information contained in the bar code symbol.
When such a bar code reader is used, for example at a point of sale, to read a bar code symbol on a product being purchased the scanning beam may not be directed exclusively at the target bar code symbol but may also scan and be reflected by bar code symbols on neighboring items which it was not intended to scan. The reflected scanning beam from the other items may be received by the decoder as a result of which incorrect information may be generated. As a specific example of such a problem, where a product being purchased is scanned at a supermarket point of sale the scanning beam may also be reflected by, for example, magazines on a magazine rack adjacent to a supermarket point of sale.
It will be appreciated therefore that the conventional bar code reading system can give rise to problems when items having bar code symbols are found adjacent or nearby the item to be scanned.
U.S. Pat. No. 5,408,080 which is incorporated herein by reference describes a bar code scanner capable of automatically scanning bar code data without a manually activated trigger to initiate a scan of bar code data. The scanner includes a light source for illuminating the bar code symbol, a photodiode array for detecting light reflected by the bar code symbol, a CCD shift register for converting the data generated in parallel in the photodiode array to a serial format and a digitizer circuit for converting the data to digital pulses. The digitized signal corresponding to the serial data is produced during a read-out period and the signal is examined to establish whether a valid bar code symbol has been read; a valid bar code symbol is indicated when the signal comprises a given number of pulses (for example, eight pulses) each pulse corresponding to a bar in the bar code symbol. The scanner continues to scan until a valid bar code symbol has been identified at which point the scan cycle is terminated. The scan cycle is recommenced after a predetermined number of successive read-out intervals following the reading of the valid bar code symbol. In order to ensure that the same bar code is not read again the number of pulses in each of the predetermined number of read-out intervals is monitored. U.S. Pat. No. 5,408,080 relates only to a static beam or field of view optical reading system.
U.S. Pat. No. 5,324,924, which is commonly assigned with the present application and incorporated herein by reference, describes an arrangement for decoding of bar code symbols in which a symbol is scanned by a light beam, light reflected from the symbol is sensed by a detector and the detected time widths (the length of time spent by the scanning light beam traversing a bar or space) are compared with a threshold value to determine if the bar code symbol is within the working range of the bar code scanner. For example, if the detected time width is smaller than a predetermined threshold value then a bar code symbol is outside a predetermined distance zone. A second evaluation is then performed to establish whether the detected bar code symbol is a valid bar code symbol i.e. it has all of the characteristics of a valid bar code symbol (for instance a check may be carried out to ensure that the detected bar code symbol has a sequence of bar and space widths which conform to the methodology of acceptable bar code symbols). Once a successful scan of a given bar code symbol has taken place any scans of an identical bar code symbol within a predetermined time is ignored on the assumption that it is the same bar code symbol that is being read. In a preferred embodiment the arrangement is provided in a gun-shaped device having a trigger allowing manual activation of the scanning light beam.